With the increasing application of arterial grafts and thrombendarterectomy for the treatment of occlusive arterial disease, the number of patients in whom the use of anticoagulant drugs might be considered beneficial in the postoperative period has increased. The action of these drugs in altering the clotting mechanism so that there is a reduced tendency for clot formation in diseased or injured blood vessels or at vascular anastomoses has been well recognized. The use of heparin and the prothrombin-depressing drugs has been established in the treatment of myocardial infarction, venous thrombosis, and peripheral arterial thromboembolism.10-13,22,29,34,55,60,65,70-72 Ever since Murray44,45,47 reported satisfactory results with the administration of heparin in association with blood vessel surgery there has been a general acceptance of the value of this agent for irrigating the open lumen of a blood vessel during the performance of an anastomosis, for the irrigation of catheters left in blood vessels, for